From AVRFreaks Wiki

[edit] Some Frequently-Asked Questions about AVR-GCC (& possibly some helpful Answers)

1. Why don't I see the C source lines interspersed with the assembly code in my .lss listings?

   Version 20071221 of WinAVR has a version of avr-objdump (from binutils 2.18) which needs to see source files with Unix line endings (LF). If your source files have DOS line endings (CRLF), avr-objdump won't show the lines in the diassembler listing. Use a good text editor or a utility such as dos2unix to convert them.